The toxic factors in the venoms of marine snails of the genus Conus will be isolated and characterized. One class of toxins from Conus geographus venom, whose structure has been elucidated will be modified to determine which residues in these peptide toxins are important for biological activity. A particularly high priority will be to find modifications that will allow radioactive labeling of toxin without a significant loss of biological activity. The other toxins in the venom of Conus geographus (one peptide toxin which acts on the peripheral neuromuscular system, and two other toxins which act only on the central nervous system) will be purified and characterized biochemically. In addition, the biochemical work on the toxins of Conus magus venom will be continued. It is clear that most of the toxins present in this second species of Conus are completely unrelated to the factors in the Conus geographus venom.